iOS-无限时后台

创建一个计时器放到NSRunLoop中 修改 UIBackgroundTaskIdentifier状态

@property (nonatomic, strong) NSTimer *timer;
@property (nonatomic, assign) UIBackgroundTaskIdentifier bgTask; //用于申请后台时间

- (void)applicationDidEnterBackground:(UIApplication *)application {
    
    self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(logAgain:) userInfo:nil repeats:YES];
    [[NSRunLoop mainRunLoop] addTimer:_timer forMode:NSDefaultRunLoopMode];
    
    UIApplication* app = [UIApplication sharedApplication];
    self.bgTask = UIBackgroundTaskInvalid;
    __weak __typeof (&*self)weakSelf = self;
    self.bgTask = [app beginBackgroundTaskWithExpirationHandler:^{
        [[UIApplication sharedApplication]endBackgroundTask:self.bgTask];
        dispatch_async(dispatch_get_main_queue(), ^{
            if (weakSelf.bgTask != UIBackgroundTaskInvalid) {
                weakSelf.bgTask = UIBackgroundTaskInvalid;
            }
        });
        
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
            if (weakSelf.bgTask != UIBackgroundTaskInvalid) {
                weakSelf.bgTask = UIBackgroundTaskInvalid;
            }
        });
    }];
}

- (void)logAgain:(NSTimer*)timer{
    //无限后台
}


- (void)applicationWillEnterForeground:(UIApplication *)application {
    if (self.timer != nil) {
        [self.timer invalidate];
        self.timer = nil;
    }
}